Unit 15 Geometric Dimensioning and Tolerancing 273 Copyright Goodheart-Willcox Co., Inc. Using position tolerancing to define location requirements provides benefits over the application of directly toleranced coordinate dimensions. Using coordinate dimensions with plus and minus tolerances to define location requirements establishes a square tolerance zone. See Figure 15‑27. The tolerance zone established by position toler- ancing is round. See Figure 15‑28. Specifying a round tolerance zone as compared to a square tolerance zone increases the area of the zone by 57%. Notice that the true position of the hole is located by basic dimensions. Position tolerances are commonly used to specify location requirements for holes. Position tolerances are also used to control coaxial relationships and sym- metrical relationships between features. Position tol- erancing is applied on an MMC, LMC, or RFS basis. A position tolerance is assumed to apply RFS unless a material condition modifier is shown in the feature control frame. When the tolerance is to apply at MMC or LMC, the appropriate modifier is shown after the tolerance value. Boundary of tolerance is parallel to datum surface Drawing Interpretation .002 tolerance zone Goodheart-Willcox Publisher Figure 15-26. Parallelism of a surface. Max. Tolerance = 1.4 × .020 = .028 Tolerance zone Drawing Interpretation Goodheart-Willcox Publisher Figure 15-27. The tolerance zone established by directly toleranced coordinate dimensions is a square zone.